The use of pyrometry for non-invasive temperature measurement and control is a necessity for some semiconductor processing applications such as Rapid Thermal Processing (RTP). Pyrometry involves measuring light emission from a silicon wafer using an infrared detector in a specified spectral band and to compute wafer temperature based on the measured radianie data. An important aspect of the pyrometric setup is the means by which light is collected from the wafer and transferred to the detector. The mounting of the pyrometer/detector somewhat away from the immediate vicinity of the process chamber window is desired to minimize the ambient temperature changes in the detector hardware. Moreover, advanced multi-zone temperature control methods require multi-point sensors which can provide good spatial resolution for mapping the wafer temperature. Hence, a light pipe has been used, especially where other equipment or space constraints require the pyrometer to be at some distance from the chamber process window. Light pipes have been used previously in semiconductor processing reactors. In some instances a simple hollow light pipe is used, i.e. the pyrometer looks at the wafer through a hollow pipe. Other applications have used a bare sapphire rod extended into the process chamber as a light pipe. In the former case the signal level is degraded because of the inevitable small angle of view and the small amount of light collected. Moreover, hollow light pipes can cause measurement error and drift due to the fact that the effective light pipe transmission is affected by the reflectivity of the light pipe wall. The latter approach, while it does maintain an acceptable signal level, is susceptible to measurement noise introduced by the direct heating of the light pipe material. The change in refractive index of the light pipe material, e.g. sapphire, at the operating wavelength range, with temperature, can cause significant temperature measurement errors unless corrected for. Further, the relatively high temperature that the light pipe is subjected to may preclude certain materials, than sapphire, from being utilized in the light pipe, e.g. fluoride or chalcogenide glass fibers. Moreover, the light pipes of prior art (e.g., sapphire rod) do not provide the spatial resolution necessary for multi-point wafer temperature measurements.